Discovery of d-orbital order in Tb2CoAl4Ge2

Zhanyang Hao; Haohao Sheng; Wanru Ma; Wengen Zheng; Yongqing Cai; Zijuan Xie; Wanlin Cheng; Zuowei Liang; Wu Xie; Wenjuan Zhao; Chen Liu; Zhibin Su; Junhao Lin; Liusuo Wu; Zhengtai Liu; Mao Ye; Ji Dai; Massimo Tallarida; Shengtao Cui; Yogendra Kumar; Kenya Shimada; Kenichi Ozawa; Shuki Torii; Kazuhiro Mori; Yue Xie; Junze Deng; Jiaou Wang; Xuetao Zhu; Jiandong Guo; Jiawei Mei; Zhenyu Wang; Xianhui Chen; Ping Miao; Zhijun Wang; Chaoyu Chen

arXiv · 2605.26426

Discovery of d-orbital order in Tb2CoAl4Ge2

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Abstract

Orbital order describes a quantum state where occupied orbitals line up in a periodic pattern. While orbital physics plays a fundamental and universal role in strongly correlated electron systems, the existence and particularly the band structure fingerprint of orbital order remain a long-standing mystery. Here, we report the discovery of rare earth 5d-orbital order developed by the surface states of intermetallic compound Tb2CoAl4Ge2. Angle-resolved photoemission spectroscopy reveals characteristic nematic features like Fermi surface deformation and band split. These experimental observations can be described by a ferro-orbital order term in the mean-field Hamiltonian. The structural and magnetic origin of such order is excluded by systematic high-resolution neutron powder diffraction and scanning tunnelling microscopy measurements. Our results provide strong evidence for a pure surface orbital order scenario avoiding complications from structural distortion as in colossal magnetoresistance manganites, magnetic order as in iron-based superconductors, and charge transfer p-orbital order in cuprates.

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Zhanyang Hao, Haohao Sheng, Wanru Ma, Wengen Zheng, Yongqing Cai, Zijuan Xie, Wanlin Cheng, Zuowei Liang, Wu Xie, Wenjuan Zhao, Chen Liu, Zhibin Su, Junhao Lin, Liusuo Wu, Zhengtai Liu, Mao Ye, Ji Dai, Massimo Tallarida, Shengtao Cui, Yogendra Kumar, Kenya Shimada, Kenichi Ozawa, Shuki Torii, Kazuhiro Mori, Yue Xie, Junze Deng, Jiaou Wang, Xuetao Zhu, Jiandong Guo, Jiawei Mei, Zhenyu Wang, Xianhui Chen, Ping Miao, Zhijun Wang, Chaoyu Chen. 2026-05-26. Discovery of d-orbital order in Tb2CoAl4Ge2. https://arxiv.org/abs/2605.26426

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